Which type of antibody causes hemolytic disease of the newborn?

Hemolytic disease of the newborn (HDN) is primarily caused by the presence of IgG antibodies in the maternal plasma that can cross the placenta. This occurs particularly in cases of Rh incompatibility or when there are ABO blood group incompatibilities between the mother and the fetus.

When an Rh-negative mother carries an Rh-positive fetus, the mother may produce IgG antibodies against the Rh factor, especially if she has been sensitized due to a previous pregnancy or blood transfusion. If these IgG antibodies pass through the placenta, they can bind to the fetal red blood cells, leading to their destruction (hemolysis), resulting in anemia, jaundice, and other complications in the newborn.

In contrast, other types of antibodies do not play a significant role in causing HDN. IgM antibodies are typically too large to cross the placental barrier and therefore do not directly contribute to this condition. IgE antibodies are primarily involved in allergic reactions and defense against parasitic infections, while IgA antibodies are mainly found in mucosal areas and in secretions such as breast milk, providing localized immunity rather than systemic effects like those seen in hemolytic disease of the newborn.